Alpha+ B218 Compact Horn Loaded Bass Module 2x18" SubwooferThe B218 Bass module uses two high force 18 drivers coupled in a common cavity loaded with a symmetric bass horn, computer optimised to guarantee ultra low distortion, even at very high levels. Using a 15 mm custom made bent plywood shell, with Poplar veneer for the inside layers and Birch for the outside, the B218 weighs in at 77kg 170lbs and achieves a peak SPL of 146dB. The low frequency horn ensures maximum radiating surface and high efficiency.